This invention relates generally to electrical wiring devices, such as electrical receptacles, switches, and the like and more particularly to wiring devices with a clamp for the ground connections to such devices.
Electrical wiring devices such as outlets, switches, receptacles and the like are commonly provided with screws having enlarged heads under which the bare end of an electrical wire can be captured to form an electrical connection to the device. Wiring devices of the type to which this invention pertains include at least three terminals, a load terminal, a neutral terminal, and a ground terminal. Connections must be made to all three of these terminals in normal use of the wiring device.
Heretofore, clamping plates have sometimes been provided for the load and neutral connections to a wiring device. However, there are special considerations associated with the connection made to the ground terminal of the wiring device that have precluded the use of clamps. When an electrical device is connected in series with other devices, it is desirable to maintain ground continuity through the series string of devices, even when one of the devices is removed. If the ground connections to the wiring device are made by way of two separate connections, then continuity may not be maintained. It is desirable to remove the insulation from a continuous length of ground wire and make the connection to the wiring device without electrically separating the ground wire at the device. In order to encourage this kind of connection, electrical wiring devices are preferably provided with a single screw for making a ground connection to the device, and moreover they are not provided with a clamping plate because the use of a clamping plate at a ground terminal would encourage or at least facilitate the connection of two separate ground wires to the ground terminal, which could be separated when the wiring device was removed or replaced, thus causing a discontinuity in the ground connection at other series connected wiring devices.
When stranded electrical wiring is used to form connections to wiring devices, and particularly when a stranded wire is used for the last electrical wiring devices in a series string of wiring devices, a screw, even a screw with an enlarged head, is not entirely satisfactory for connecting the stranded wire to the wiring device. Even if the strands of the wire are twisted before a connection is made, pressure between the head of the screw and the stranded wire often cause strands to become disassociated from the bundle of remaining strands, and an unsatisfactory connection is thereby made.
It is an object of this invention to provide a wiring device that overcomes the problems of prior art wiring devices, especially with respect to making ground connections to such devices.
Briefly stated, and in accordance with a presently preferred embodiment of this invention, a wiring device comprises a good plate to which a ground connection is to be made; a treaded opening in the ground plate; a screw engaged with the threaded opening and having an enlarged head; a pressure plate having an opening therethrough and engaging the screw between the screw head and the ground plate of the wiring device; and cooperating means on the ground plate and the pressure plate for substantially preventing rotation of the pressure plate relative to the ground plate when the screw signal is engaged with the pressure plate.
In accordance with another aspect of this invention, the pressure plate includes a bull nose for guiding a wire attached to the wiring device into a fixed location relative to the pressure plate.
In accordance with still another aspect of this invention, the pressure plate includes a cut away region for substantially preventing two separate wires from being simultaneously engaged by the pressure plate, one on each side of the screw.
The novel aspects of the invention are set forth with particularity in the appended claims. The invention itself, together with further objects and advantages thereof may be more readily comprehended by reference to the following detailed description of a presently preferred embodiment of the invention.